1. Field of the Invention
The present invention relates to a reclining device for a vehicle seat such as an automotive seat.
2. Description of Prior Art
In a typical conventional reclining device used in a vehicle seat, a pair of lock gears are provided for their mutual meshed engagement to place the reclining device in a locked state, so that a seat back may be adjustably locked at a desired inclination angle relative to a seat cushion. The reclining device has an arm plate rotatably fixed to the seat back, which arm plate is provided with one of those two lock gears, and has an operation lever operatively connected to a lock plate provided with another of the same lock gears, as is known, for example, from the Japanese Laid-Open Patent Pub. No. 57-134340. Because of the two lock gears being in a partial mesh with each other, a weight of a passenger is directly exerted via the seat back upon the meshed part between the two lock gears, and therefore, both lock gears require a sufficient strength to resist such passenger's weight. This is an important issue calling for a high safety of vehicle or automobile, in view of an excessive load or passenger's weight tending to give an extraordinary impact to the seat back in such a case of a sudden acceleration or deceleration. Consequently, the teeth of the lock gear need to be formed more greatly in thickness than normally considered.
Such formation of lock gear inevitably results in increasing the dimensions of the lock gear per se, which means to make larger the whole body of reclining device, thus taking up much space for mounting the reclining device in the seat. Obviously, not only the outer aesthetic appearance of seat is impaired, but also is deteriorated the cushiony property of the seat. Further, the increase in thickness of each lock gear tooth results in giving a large pitch between one and another teeth, which undesirably increases the interval per degree a for reclining angle of the seat back relative to the seat cushion, leaving a problem with a fine adjustment of the reclining device.